(1) Field of the Invention
The present invention relates to a mobile track tamping machine comprising a machine frame, undercarriages mounting the machine frame on a track for mobility in an operating direction, the track being comprised of two rails fastened to ties supported on ballast, each rail having a gage side and a field side, and a plurality of independently transversely and vertically adjustable tamping tool units aligned transversely to the track, each tamping tool unit comprising a pair of reciprocable vibratory tamping tools including tamping picks immersible in the ballast, drive means for reciprocating the tamping tools in a direction extending substantially perpendicularly to the ties and for vibrating the tamping tools, and a drive for vertically adjusting the tamping tool unit.
(2) Description of the Prior Art
A mobile track tamping machine of this general type is known, for example, from U.S. Pat. No. 3,534,687, dated Oct. 20, 1970. This machine comprises two cantilevered carrier frames for two tamping tool units, each comprising two sequentially arranged pairs of reciprocatory and vibratory tamping tools for simultaneously tamping two adjacent ties. The carrier frames are mounted on a machine frame portion which is laterally pivotal about a vertical axis and are independently transversely displaceable on the machine frame portion by independent transverse adjustment drives. The tamping tool picks are independently laterally pivotal and this machine, with its cantilevered tamping tools, may be used for tamping ties in switches and as a track leveling, lining and tamping machine when combined with a leveling and lining reference system.
U.S. Pat. No. 3,426,697, dated Feb. 11, 1969, also relates to a switch tamper with a cantilevered tamping tool arrangement, i.e. a type of tamper hardly used any more for about twenty years. Respective tamping tool units associated with each track rail are mounted on an elongated carrier frame which is pivotal about a vertical axis on the machine frame and the vertically adjustable tamping tool units are independently transversely displaceable on the carrier frame, the arrangement being designed to enable the tamping tools to be repositioned in encountered in switches. This structure is expensive because the pivotal carrier frame extends over the entire machine frame to the rear end thereof where it is glidingly affixed by a sliding bearing to enable the elongated carrier frame to be pivoted. Furthermore, the arrangement has the disadvantage that the tamping tools are pivoted on a common carrier frame and, therefore, cannot be properly centered with respect to the tie to be tamped since the pivoting axis of the carrier frame is spaced from the center of the transverse displacement guide. In other words, the tamping picks will not extend parallel to the tie being tamped and, therefore, the quality of tamping will be poor.
U.S. Pat. No. 4,625,651, dated Dec. 2, 1986, discloses a modern track switch leveling, lining and tamping machine of the compact type, the tamping tool units and the track lifting and lining unit being arranged between two widely spaced undercarriages, which not only enables the accuracy of leveling and lining to be enhanced considerably but also makes it possible to reduce the extent of rail bending during the track correction to a minimum because of the wide spacing of the undercarriages holding down the respective ends of the track sec ion being corrected and thereby to protect the rails from undue stresses. A carrier frame is associated with each track rail and supports a tamping tool unit and a longitudinally adjustable coupling pivotally links one end of each carrier frame to the machine frame while a free steering gear supports an opposite end of each carrier frame on the associated track rail. A track switch lifting and lining unit is also mounted on each carrier frame.
U.S. Pat. No. 4,576,095, dated Mar. 18, 1986, discloses a ballast tamping machine with two independently transversely adjustable tamping tool units, each unit comprising a pair of reciprocatory and vibratory tamping tools respectively arranged at the field side and the gage side of each track rail. Each pair of tamping tools is independently vertically adjustable so that the machine may be used even in difficult switch areas by raising any pair of tamping tools out of its operative position when it encounters an obstacle.
British patent application No. 2,201,178, published Aug. 24, 1988, deals with a switch tamper of the cantilevered type wherein four tamping tool units are independently vertically and transversely adjustable. This machine has no track lifting and lining unit. Independently adjustable tamping tool units are also known from U.S. Pat. Nos. 3,669,025, dated June 13, 1972, and No. 4,445,437, dated May 1, 1984, wherein two pairs of tamping tools are associated with each track rail, the four pairs of tamping tools form independently vertically adjustable tamping tool units and are independently transversely displaceable on a carrier frame mounted on the machine frame. While these arrangements adapt the machine for work in most switch areas, they do not work satisfactorily in areas of non-uniform crib widths and where obliquely positioned ties are to be tamped.